The invention relates to a device and a method for calibrating and balancing a measuring device of a tablet press, in particular a rotary tablet press. A rotary tablet press normally has a rotor, which is driven in a rotating manner via a generally vertical axis with a suitable drive motor. The rotor has an upper and a lower punch guide for receiving upper and lower punches. The punches work together with receivers of a die plate, which is arranged between the punch guides. Press material is fed to the receivers via suitable filling devices. The upper or respectively lower punches work together in pressing stations with upper and lower pressing rollers to compress the press material filled in the receivers into a tablet. In general, suitable control cam sections are provided, which guide the punches in the axial direction over their punch heads. For example, a filling cam section is assigned to a filling station, which ensures that the lower punches in the area of the filling cam section protrude into the receivers to a specified degree. This mass determines the fill volume and thus also the weight of the pressed tablet. The pressed tablets are stripped off the top side of the die plate in a stripping area arranged below this in the direction of rotation. A guide cam is generally provided for this, through which the lower punches are raised far enough that the tablets are captured by the stripper and can be pushed off, for example into a discharge channel. Moreover, a suitable control cam section generally ensures that the upper punches are conveyed away via a filling device. Such a tablet press is for example known from DE 10 2004 040 163 C5.
It is known to equip such rotary tablet presses with different measuring devices or respectively sensors. The measuring devices convert physical measurements into electrical signals, which are then fed to the machine controller of the rotary press and further processed there and/or displayed. The measurement signals of the measuring devices can signal for example the proper state of the rotary press. On the other hand, they can deliver measurement values for determining the quality of the pellets pressed in the press, in particular tablets. For example, measurement sensors for the stiffness of the upper and lower press punches in the punch guide and/or for the tablet discharge force can signal the state of the press. A quality determination of the produced tablets takes place for example via a pressing force measurement at the pre- and/or main pressing station.
In order to meet the strict requirements in the field of pharmaceutical production, the measuring devices must be calibrated and balanced regularly so that a continuously sufficient measurement accuracy and thus production quality is ensured. The results of this calibration are normally documented in the form of a measurement table. For example, an additional reference force measuring device (consisting of a sensor and a measuring device, in particular a measurement amplifier) is installed for example for the calibration of measuring devices arranged in the area of the pressing rollers. The distance between the upper and lower pressing roller is then reduced step by step manually by means of the adjustment drives. Both the measuring device as well as the reference force measuring device are thereby exposed to different force values. Each new force value in the course of the calibration is initiated manually and read by an operator from the measuring devices, in particular from the measuring device to be calibrated, that is in particular a measuring device permanently installed in the press, and the reference force measuring device. The number of calibration steps is normally specified by a process instruction. After each calibration step, a comparison is performed between the measurement values of the measuring device to be calibrated and the reference measuring device. In the case of impermissible deviations, the amplification factor of a measurement amplifier of the measuring device is for example also reset, i.e. balanced, manually. The finally set values are logged in a log form. Several measurement points are thereby normally initiated manually within a force range.
The disadvantage of this procedure is that it can lead to read errors by the operator. Moreover, errors may result during the manual balancing of the measuring device and the logging. The described method also takes a lot of time and punctiform deviations and non-linearities, caused for example by machine tolerances from e.g. storage and guiding, are not generally detected. The same goes for impact variables on the measuring devices, which occur during the operation of the rotary press, for example temperature deviations, wear or other disturbance variables.
Based on the described state of the art, the object of the invention is thus to provide a device and a method of the initially-named type, with which an exact and secure calibration and balancing of the measuring devices is possible in an easy and fast manner.